1. Field of the Invention
The present invention relates to a thermoplastic polymer composition having good flexibility and excellent barrier properties with respect to gases and organic liquids and suitable for adhesive bonding to polyolefin resins. The present invention also relates to a molded product composed of such a thermoplastic polymer composition and to a multilayer structure having a layer composed of such a thermoplastic polymer composition.
2. Description of the Related Art
In recent years, thermoplastic elastomers which are soft materials having rubber elasticity, require no vulcanization, and can be molded and recycled similarly to thermoplastic resins have been widely used in the fields of automobile parts, parts of electric appliances, electric cable coatings, medical components, consumer goods, footwear, and the like. Among such thermoplastic elastomers, the usage of hydrogenates of vinyl aromatic compound—conjugated diene compound block copolymers (referred to hereinbelow simply as “hydrogenated block copolymers”) has recently increased because blending a softening agent for rubber therewith increases the flexibility thereof and gives excellent rubber elasticity and moldability thereto.
However, thermoplastic elastomers such as the aforesaid hydrogenated block copolymers generally have poor barrier properties with respect to gases such as oxygen, nitrogen, and carbon dioxide, and organic liquids such as gasoline and oils. Accordingly, they are very difficult to use for sheets, films, packaging materials for food, containers, packing materials for containers, tubes, hoses, and the like, which require barrier properties with respect to such gases and organic liquids.
On the other hand, ethylene-vinyl alcohol copolymers have good barrier properties with respect to gases and organic liquids and do not generate toxic gases during incineration, as vinylidene chloride resins or vinyl chloride resins. As a result, they are widely used for a variety of applications, e.g., for packaging materials for food. However, because ethylene-vinyl alcohol copolymers have poor flexibility, they are not suitable for applications where thermoplastic elastomers have been used and where barrier properties are required.
Accordingly, an attempt has been made to obtain a material combining flexibility and barrier properties with respect to gases and organic liquids by mixing an ethylene-vinyl alcohol copolymer with another soft resin under melting conditions (Japanese Patent Application Laid-open No. H10-110086). However, due to poor mutual compatibility of ethylene-vinyl alcohol copolymer and soft resins, the product has poor mechanical properties. Yet another drawback thereof is that the product does not adhere to polyolefin resins. Furthermore, an attempt has also been made to obtain a material with excellent impact resistance and oil resistance by mixing ethylene-vinyl alcohol copolymer with a soft resin under melting conditions, wherein the soft resin was modified with an epoxy compound, in order to improve mutual compatibility of the ethylene-vinyl alcohol copolymer and the soft resin (Japanese Patent Application Laid-open No. H7-207097).
However, flexibility and adhesion to polyolefin resins was insufficient. Furthermore, it was also suggested to add a styrene-based elastomer modified with maleic anhydride for the purpose of improving mutual compatibility of ethylene-vinyl alcohol copolymer and polypropylene and improving the external appearance of the molded product (Japanese Patent No. 2612034). In this case, adherence to polyolefins is obtained, but the product is hard and demonstrates no rubber elasticity. As a result, it cannot be used as a thermoplastic elastomer.